"Contribution a l'etude theorique et experimentale du comportement mecanique d'un assemblage colle de type Tenon-Mortaise sollicite a la traction"

SIGLEINIST T 77102 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Forest ecological research in the perspective of mitigating climate change in tropical ecosystem: case study of Cameroon (Central Africa)

There is a growing recognition that climate change is an important issue that impact adversely people livelihood and sustainable development Mitigating climate change through afforestation, reforestation and reducing emissions from deforestation and forests degradation (REDD) can become key components of land use planning and land use management in several tropical countries. Challenges in most countries include the design and implementation of sound research programs that satisfy the information needs of a national and international agenda on climate change. In the perspective of guiding forest-related research activities associated with climate change mitigation, this review synthesizes past research activities and provides baseline orientation for ecological research oriented towards climate change mitigation in Cameroon. The ecological and socioeconomic diversity offered by the country offers great opportunities for pilot mitigation research initiatives that can be extrapolated in other parts of central African sub region. However there is a need for enhanced research infrastructure, financial resources and capacity building in order to ensure continuous production of new scientific informatio

Biological nitrogen fixation potential by soybeans at two lowP soils of southern Cameroon

Biological nitrogen fixation (BNF) potential of 12 soybean genotypes were evaluated in condition of low and sufficient supply in two acid soils of southern Cameroon. The P sources were Togolese phosphate rock (PR) and triple super phosphate (TSP). The experiment was carried out during two consecutive years (2001 and 2002) at two locations with different soil types. Shoot dry matter, nodule dry matter, N and P uptake were assessed at flowering and the grain yield at maturity. Shoot dry matter, nodule dry matter, N and P uptake, and grain yield significantly varied with site and genotypes (P < 0.05). On Typic Kandiudult soil, nodule dry matter ranged from 0.3 to 99.3 mg plant-1 increasing significantly with P application (P < 0.05). Total N uptake of soybean ranged from 38.3 to 60.1 kg N ha-1 on Typic Kandiudult and from 18 to 33 kg N ha-1 on Rhodic Kandiudult soil. Under P limiting conditions, BNF ranged from -5.8 - 16 kg N ha-1 significantly higher values for genotype TGm 1511 irrespective of soil type. Genotype TGm 1511 can be considered as an important companion crop for the development of smallholder agriculture in southern Cameroon

Phosphorus benefits from grain-legume crops to subsequent maize grown on acid soils of southern Cameroon

We conducted field experiments over 2 years on two acid soils of southern Cameroon to test whether efficient uptake and use of phosphorus (P) from less available sources by grain legume genotypes could benefit subsequent rotational maize. We grew two crops each year. For the first crop we grew 4 genotypes of soybean and of cowpea, plus maize. For the second crop we grew maize. The first crops were fertilized with 0, 90 kg P ha?1 as phosphate rock (PR) or 30 kg P ha?1 as triple super phosphate (TSP). P application highly significantly increased shoot dry matter, P uptake, N2 fixation and grain yields of the grain legumes with TSP generally more effective than PR. Two of the soybean and two of the cowpea genotypes were more efficient at using P. Only the P-efficient soybean and cowpea genotypes increased subsequent maize yields. Yields of the subsequent maize grown in rotation were significantly correlated with shoot P uptake for which the quantity of P applied with the crop residues of the pre-crop appeared to be a major factor. We also grew the grain legumes in nutrient solutions and measured organic acid-anion exudation from roots, root-surface phosphatase-activity, and root morphological characteristics. Enhanced exudation of organic acid anions from roots of P-deprived plants might have contributed to the P acquisition efficiency under field conditions of the P-efficient cowpea genotypes and one of the P-efficient soybean genotypes. A higher activity of root-surface acid phosphatase might have been important for the other P-efficient soybean genotype. The results show, that the potential positive rotational effect of cowpea and soybean on the acid, highly P-sorbing soils of southern Cameroon depends on breeding and using P-efficient genotypes when sparingly soluble and suboptimal rates of soluble P fertilizers are used

Conversion of lowland tropical forests to tree cash crop plantations loses up to one-half of stored soil organic carbon

Tropical deforestation for the establishment of tree cash crop plantations causes significant alterations to soil organic carbon (SOC) dynamics. Despite this recognition, the current Intergovernmental Panel on Climate Change (IPCC) tier 1 method has a SOC change factor of 1 (no SOC loss) for conversion of forests to perennial tree crops, because of scarcity of SOC data. In this pantropic study, conducted in active deforestation regions of Indonesia, Cameroon, and Peru, we quantified the impact of forest conversion to oil palm (Elaeis guineensis), rubber (Hevea brasiliensis), and cacao (Theobroma cacao) agroforestry plantations on SOC stocks within 3-m depth in deeply weathered mineral soils. We also investigated the underlying biophysical controls regulating SOC stock changes. Using a space-for-time substitution approach, we compared SOC stocks from paired forests (n = 32) and adjacent plantations (n = 54). Our study showed that deforestation for tree plantations decreased SOC stocks by up to 50%. The key variable that predicted SOC changes across plantations was the amount of SOC present in the forest before conversion—the higher the initial SOC, the higher the loss. Decreases in SOC stocks were most pronounced in the topsoil, although older plantations showed considerable SOC losses below 1-m depth. Our results suggest that (i) the IPCC tier 1 method should be revised from its current SOC change factor of 1 to 0.6 ± 0.1 for oil palm and cacao agroforestry plantations and 0.8 ± 0.3 for rubber plantations in the humid tropics; and (ii) land use management policies should protect natural forests on carbon-rich mineral soils to minimize SOC losses